Preloaded table coupling

Abstract

Table couplings for coupling hydraulic actuators to large shaking tables, such as earthquake simulator tables are preloaded under gaseous pressure to permit the couplings to be nontension carrying couplings, which in turn permits use of hydrostatic slip bearings between the side surfaces and the bottom surface of the table and the actuators. The hydrostatic bearings in turn reduce the need for swivels, links and yokes that carry both tension and compression. The use of compression only loading such as that permitted with the present device, also reduces the problem of making a satisfactory table foundation, because only compression loads are carried to the foundation rather than alternating tension-compression loads.

What is claimed is: 
     
       1. In an actuator system for a rigid shaker test table including first actuator means for supporting the weight of the table for movement generally in vertical directions, and second actuator means for controlling the horizontal movement of the table comprising a plurality of oppositely disposed actuators on opposite sides of the table, the improvement comprising each of the second actuator means including a rod and having two actuator sections, a coupling for transferring force from the rod of each second actuator means to the table, the first of the sections for each second actuator means comprising a chamber, means to provide a compressible fluid under pressure to each chamber for exerting a load controlled by the fluid under pressure on the rod of each of the second actuator means toward a table with which the second actuator means are used under a substantially steady controlled load on the coupling between the respective rod and such table to carry a compression load to such table, and each second actuator means including a dynamic section for exerting a cyclic load on the respective rod which varies to be in addition to and subtracted from the load exerted on the rod and coupling by the first section of each second actuator means as the table is moved by the dynamic section of the second actuator means, each coupling comprising a separate hydrostatic bearing means coupled to the respective rods of each second actuator means and engaging surfaces movable with the table, said hydrostatic bearing means including two sections having mating surfaces that permit swiveling of a table relative to a respective second actuator means throughout a desired range of movement thereof and providing hydrostatic sliding bearings which carry compression loads only relative to such table, the cyclic load subtracted from the load of the first actuator section being less than the load exerted by the first actuator section to maintain compression loads on the hydrostatic bearing means. 
     
     
       2. In an actuator system for a rigid shaker test table including first actuator means for supporting the weight of the table for movement generally in vertical directions, and second actuator means for controlling the horizontal movement of the table comprising a plurality of oppositely disposed second actuators on opposite sides of the table, the improvement comprising each of the actuator means including a rod and having two actuator sections, a coupling for transferring force from the rod to the table, the first of the sections of each actuator means comprising means for providing a pressure controlled by gaseous fluid under pressure for exerting a load on the rod of each of the actuator means toward a table with which the actuator means is used under a substantially steady load to the coupling between the respective rod and such table to carry a compression load to such table, and each actuator means including a second dynamic section for exerting a cyclic load which varies to be in addition to and subtracted from the load exerted on the rod and coupling by the first section of each actuator means as the table is moved by the dynamic section of the respective actuator means, the cyclic load subtracted from the load of the first section of the second actuators being less than the load exerted by the first section of the second actuators to maintain compression loads on the couplings of the second actuators, and the first gaseous fluid sections of two oppositely disposed second actuators being connected fluidly together to provide gaseous fluid flow and substantially equal pressure of gaseous fluid between the connected first gaseous fluid sections of two second actuators, one on each of the opposite sides of the table. 
     
     
       3. In an actuator system for a rigid shaker test table including first actuator means for supporting the weight the table for movement generally in vertical directions, and second actuator means for controlling the horizontal movement of the table comprising a plurality of oppositely disposed second actuators on opposite sides of the table, the improvement comprising each of the second actuator means including a rod and having two actuator sections, a coupling for transferring force from the rod to the table, the first of the sections of each second actuator means comprising means for providing a pressure controlled by a gaseous fluid under pressure for exerting a load on the rod of each of the second actuator means toward a table with which the second actuator means is used under a substantially steady load to the coupling between the respective rod and such table to carry a compression load to such table, and each second actuator means including a second dynamic section for exerting a cyclic load which varies to be in addition to and subtracted from the load exerted on the rod and coupling by the first section of each second actuator means as the table is moved by the dynamic section of the respective actuator means, the cyclic load subtracted from the load of the first section of the second actuator means being less than the load exerted by the first section of the second actuator means to maintain compression loads on the couplings of the second actuator means, the first actuator means for supporting the weight including a first gaseous fluid section for applying a load onto such table that supports the table in use, and each coupling comprising separate hydrostatic bearing means coupled to the respective rods of each actuator means, the hydrostatic bearing means engaging surfaces movable with the table, said hydrostatic bearing means providing hydrostatic sliding bearings which carry compression loads only relative to a table with which they are used, and said first sections of each actuator means providing a preload sufficient to maintain the hydrostatic sliding bearings under compression as the respective actuator means are cycled. 
     
     
       4. The apparatus as specified in claim 3 wherein said hydrostatic bearing means include two sections having mating surfaces that permit swiveling of a table relative to a respective actuator means throughout a desired range of movement thereof. 
     
     
       5. The apparatus of claim 3 and hold-down cylinder mean connected to exert a force from a pressure controlled by a gaseous fluid, the hold-down cylinder exerting a force on the table which keeps the couplings between the first actuator means and the table under compression during operation.